A. Inflammatory Response Results in Activation of Macrophages
Microbial infections of various tissues cause inflammation which results in chemotaxis and activation of phagocytes. Inflamed tissues release lysophospholipids due to activation of phospholipase A. Inflamed cancerous tissues produce alkyl-lysophospholipids and alkylglycerols as well as lysophospholipids, because cancerous cells contain alkylphospholipids and monoalkyldiacylglyercols. These lysophospholipids and alkylglycerols, degradation products of membranous lipids in the inflamed normal and cancerous tissues, are potent macrophage activating agents (Yamamoto et al., Cancer Res. 7:2008, 1987; Yamamoto et al., Cancer Immunol. Immunother. 25:185, 1987; Yamamoto et al., Cancer Res. 24:6044, 1988).
Administration of lysophospholipids (5-20 .mu.g/mouse) and alkylglycerols (10-100 ng/mouse) to mice activates macrophages to phagocytize immunoglobulin G-coated sheep red blood cells. The macrophages phagocytize the target red blood cells via their receptors recognizing the Fc portion of the immunoglobulin G but not the C3b portion of the complement (Yamamoto et al., Cancer Res. 47:2008, 1987).
In vitro treatment of mouse peritoneal macrophages alone with lysophospholipids or alkylglycerols results in no enhanced ingestion activity (Yamamoto et al., Cancer Res. 48:6044, 1988). However, incubation of peritoneal cells (mixture of macrophages and B and T lymphocytes) with lysophospholipids or alkylglycerols for 2-3 hours produces markedly enhanced Fc-receptor-mediated phagocytic activity of macrophages (Yamamoto et al., Cancer Res. 47:2008, 1987; Yamamoto et al., Cancer Res. 48:6044, 1988).
Incubation of macrophages with lysophospholipid- or alkylglycerol-treated B and T lymphocytes in a medium containing 10% fetal calf serum developed a greatly enhanced phagocytic activity of macrophages (Yamamoto et al., Cancer Res. 48:6044, 1988; Homma and Yamamoto, Clin. Exp. Immunol. 79:307, 1990). Analysis of macrophage activating signal transmission among the nonadherent (B and T) lymphocytes has revealed that lysophospholipid- or alkylglycerol-treated B-cells can transmit a signalling factor to T-cells; in turn, the T-cells modify the factor to yield a new factor, which is capable of the ultimate activation of macrophages for ingestion capability (Yamamoto et al., Cancer Res. 48:6044, 1988).